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Translation of abstract (English)

Many heterogeneous catalysts used in industry today consist of nanometer-sized particles of a catalytically active material anchored to a support. One major problem that occurs in such catalyst systems is aging, which is characterized by agglomeration of the catalytically active species (Pt, for example) at elevated operation temperatures. The catalysts become less active due to the reduction in surface area to volume ratio, which is directly correlated with their activity. An approach to overcome the agglomeration could be mixing a second metal element to the catalytically active material, due to its stabilizing effects. Indeed, adding a second metal element to catalytically active nanoparticles is one way of improving their catalytic properties as well as their stability. Bimetallic nanoparticles combine size with various composition effects, giving them new physical and/or chemical properties that could not be obtained by varying either of them individually. Optimal size, structure and percentage composition of the catalytically active bimetallic nanoparticles are usually related.
Recently, several preparation techniques have been developed to produce monodisperse metal nanoparticles in order to study how particle size, composition and morphology affect catalytic performance. However, aggregation remains a major problem in the deposition of nanoparticles onto solid substrates. Block Copolymer Micelle Nanolithography (BCMN) is one way to deposit nanoparticles in a controlled manner on solid substrates.
In this thesis BCMN was developed further in order to synthesize separated, monodisperse and thermally stable bimetallic nanoparticles consisting of different transition metals like Au, Pt, Pd, Rh, Ni and Ag with varying percentage compositions not only on planar substrates but also on microspheres and mesoporous catalyst supports. For this, polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) micelles dissolved in toluene were loaded with two different metal precursors. Planar substrates were either dip coated or spin coated whereas powder-like substrates were flushed with the micellar solution. Subsequent hydrogen plasma treatment was employed for removing the polymer and co-reducing the metal precursors. The bimetallic nanoparticles produced with the same diblock copolymer were separated and uniform in size and shape. HRSTEM-EDX studies revealed that the particles exhibited a random alloy-type structure although some of the combinations of metals (Au and Pt, for example) are known to be largely immiscible in bulk and tend to form a core@shell architecture at the nanoscale. The percentage compositions of the alloy nanoparticles could easily be adjusted by the loading ratio of the micelles with the corresponding metal precursors. Even when the alloy particles were annealed to temperatures as high as 750 °C for 7 h under ambient pressure and moisture the two components did not segregate into a core@shell morphology. This is contrary to what is predicted by current theory. Moreover, annealing caused AuPt, NiPt and RhPt alloy particles to become partially embedded in silica substrates. The initial particle pattern obtained via BCMN remained on the substrate surfaces and the alloy particles were prevented from agglomerating. Alloying of Pt with a second metal element resulted in a thermal stabilization without further treatment with stabilizing agents or additional stabilization procedures.
The work presented in this thesis demonstrates a simple and effective route to the fabrication of thermally stable alloy nanoparticles of different transition metals with varying percentage compositions on planar and 3D substrates. Segregation of the metals and agglomeration of the synthesized alloy particles is prevented due to their partially embedding into silica substrates during annealing. The synthesized particles show potential as heterogeneous catalysts, especially for thermal conversions.